1. Field of the Invention
The present invention relates to a method and apparatus for enhancing transmission efficiency in a wireless communications system, and more particularly, to a method and apparatus for decreasing overhead and transmission time, and enhancing transmission efficiency.
2. Description of the Prior Art
The third generation (3G) mobile communications system has adopted a Wideband Code Division Multiple Access (WCDMA) wireless air interface access method for a cellular network. WCDMA can provide high frequency spectrum utilization, universal coverage, and high quality, high speed multimedia data transmission. The WCDMA method also meets all kinds of QoS requirements simultaneously, providing diverse flexible two-way transmission services and better communication quality to reduce transmission interruption rates.
The Access Stratum (AS) of the 3G mobile communications system comprises various protocol stacks, such as Radio Resource Control (RRC), Radio Link Control (RLC), Media Access Control (MAC), Packet Data Convergence Protocol (PDCP), and Broadcast/Multicast Control (BMC). In addition, the 3G mobile communications system also provides different levels of transmission quality, and can operate in different corresponding modes according to different transmission quality requirements, such as: Transparent Mode (TM), Unacknowledged Mode (UM), and Acknowledged Mode (AM). TM is appropriate for use in services with high requirements for real-time transmission, UM is appropriate for use in services with requirements for real-time transmission and packet sequencing, and AM is appropriate for use in services with low requirements for real-time transmission, but high requirements for data accuracy.
In addition, the 3G mobile communications system can provide Multimedia Broadcast and Multicast Service (MBMS), which transmits service content (e.g., television programs, movies, commercials) from servers to each user equipment (UE) through different cells in Unacknowledged Mode (UM). Each UE may be located under coverage of many different cells. In other words, a UE can receive a same service content from different cells. Thus, in order to correctly process the service content and take advantage of this multi-route transmission characteristic, the prior art provides a Duplicate Avoidance and Reordering (DAR) function in UM RLC entity, to efficiently combine Protocol Data Units (PDUs) that may be transmitted from different sources (cells) and/or retransmitted from a same source, to form a PDU sequence with a correct order. After initiating the DAR function, the RLC entity executes duplicate PDU detecting, discarding and reordering operations according to Sequence Numbers (SNs) of the PDUs.
The DAR function can decrease block error rate of MBMS point-to-multipoint Traffic Channel (MTCH), which supports data transmission in MBMS services. Besides, the prior has applied the DAR function on Common Control Channel (CCCH), to decrease error rate of control messages transmitted on the CCCH, so as to decrease transmission time.
In order to apply the DAR function on CCCH, the upper layer (e.g. RRC layer) needs to send specified signaling, such as IE “DL Duplication Avoidance and Reordering info”, to UM RLC entity, which increases overhead and decreases transmission efficiency.